Classification of Forearm Involvement in Multiple Hereditary Exostoses: Consensus from the CoULD Study Group.

Background: Existing classifications for forearm deformity in multiple hereditary exostoses (MHE) have demonstrated low interrater reliability and limited clinical applicability. Our primary research question was whether a Delphi consensus process could generate a more reliable and clinically useful classification for longitudinal surveillance of MHE-related forearm deformities.

Methods: Fifteen pediatric hand surgeons from the Congenital Upper Limb Difference (CoULD) Study Group participated in 7 rounds of online Delphi surveys (June 2022 to September 2023). An investigator team facilitated the process with anonymized feedback. Round 1 identified key clinical and radiographic features. Subsequent rounds refined these features, determined categorical structure, and piloted the system with representative radiographs. Consensus was defined as ≥70% agreement. After final consensus, interrater reliability was tested by 4 independent surgeons who classified 101 radiographs from 67 patients with forearm MHE. Reliability was assessed with kappa and concordance coefficients and compared with the Masada, Gottschalk, and Jo classifications.

Results: The Delphi process identified radiographic predictors that included ulnar variance, the radial articular angle (RAA), radial head alignment, and osteochondroma size. Consensus favored a 3-tier classification: Type 1, mild; Type 2, moderate; and Type 3, severe. Closing consensus was achieved, with 93% agreement. Reliability testing showed moderate agreement on the first reading (kappa = 0.55), significantly higher than for the Masada (kappa = 0.21 [original classification], kappa = 0.35 [modified version]), Gottschalk (kappa = 0.43), and Jo (kappa = 0.43) classifications. After refinement that incorporated osteochondroma size and the radial head subtypes (3A, subluxation, and 3B, dislocation), agreement improved to substantial (kappa = 0.64) (p < 0.001), with high concordance (0.82).

Conclusions: The CoULD MHE Classification, developed through expert consensus, integrates validated radiographic predictors with defined thresholds. It demonstrated significantly improved reliability over prior systems and provides a practical framework for longitudinal monitoring of forearm deformities in patients with MHE.

Level of evidence: Diagnostic Level V. See Instructions for Authors for a complete description of levels of evidence.